Add link to download sha256 checksum

[goyalyashpal]

Continuation of https://github.com/wez/wezterm/issues/2114

This is more like a reminder... as:

• i dont know the specifics, and we can go back and forth on this,
• but i guess it would be much much faster if u do it alone too, as you know all the details of it

that's why i did not write this for all operating systems too....

destination:

• https://wezfurlong.org/wezterm/install/windows.html
• https://github.com/wez/wezterm/tree/main/docs/install

[goyalyashpal]

oops, wrong commit message....

feel free to squash these commits if you feel so

[wez]

Can you build the docs and capture a screenshot of how that changed page looks? I think it will look a bit odd!

These are the steps used by the CI: https://github.com/wez/wezterm/blob/main/.github/workflows/pages.yml#L36-L51

Install prerequisites:

cargo install mdbook --no-default-features --features search --vers "^0.4" --locked
cargo install mdbook-linkcheck --locked
cargo install mdbook-mermaid --locked
cargo install gelatyx --locked

Then to build:

./ci/build-docs.sh

You can run them locally:

mdbook serve docs